It is desirable to use a fiberglass mat to reinforce an organic polymer matrix, or plastics, to provide the resultant products with dimensional stability, strength and toughness. When used to make complex curved, curved in more than one direction, or deep drawn parts, it is necessary that the bond between glass fibers is sufficiently elastic to allow the mat to stretch or compress to the dimension of the part being made. Chopped strand mat and continuous strand mat have traditionally been used for making such parts in the past. These mats are made by bonding strands, made up of about 20 or more chopped or continuous fibers, with a binder that will dissolve in or be softened by the polymer matrix that the mat will reinforce, or in the alternative the bonds holding the fiber strands together are so weak that many will be broken by the stress from forming the reinforced part, allowing the some or all of the fiber strands to move with the polymer matrix surrounding the fiber bundles.
It is desirable to use nonwoven mats made from a wet process which disperses the fibers to form a web of crisscrossing monofilaments containing at most only a small percentage of bundles of only a few fibers. Such nonwoven mats are usually more uniform in basis weight, weight of mat per unit area, than chopped strand mats or continuous strand mats, and are thinner. A problem with using such mats in such an application has been that they do not stretch or compress with the forming stresses, but instead tend to tear or to crease and fold, all of which are unacceptable for a reinforcing mat. This occurs because the binders used to hold the mono-filaments together do not have the necessary elasticity, even when coated with the polymer matrix. It is known to use a binder that dissolves in styrene to allow the bonds to be broken and the fibers to move, but this often leads to torn mat or mat that has too little strength to perform in the molding or forming process.
When making parts that require electrically conductive surfaces and/or interior, it has been common practice to add a conductive agent like carbon or metal powder or carbon fiber to the polymer matrix or to add carbon fibers to a nonwoven web or mat, such as shown in U.S. Pat. No. 5,368,913. This patent discloses a process in which a plurality of electrically conductive filaments are distributed into a nonwoven fabric as the fabric is being made. The filaments can be carbon or metal. The problem with such a process for making a conductive mat is that if enough conductive fibers are used to make a web having uniform conductive properties, the web takes on the characteristics of the conductive fibers instead of the non conductive fibers which are desired. Also, the conductive fibers tend to be denser and/or more expensive than the non conductive fibers, thus making the mat heavier and more expensive than feasible. Finally, carbon fiber is not suitable for making antenna dishes because the carbon fiber absorbs the signal waves instead of reflecting the signal which is essential.
It is also known to use metallized resin fibers as conductive fibers in a nonwoven material as disclosed in U.S. Pat. No. 5,202,536. Currently satellite antenna dishes are made with sheet molding compound and a woven metal wire screen or perforated metal sheet, but these conductive materials are expensive and difficult to mold. It would be preferable to use a conductive fiber glass nonwoven mat because of its lower cost and desired compatibility with SMC compound instead of the metal screen or perforated sheet, but such a conductive fiber glass mat is not available. Also, while the metal woven screen and perforated metal sheet will stretch to form a complex curve like a dish antenna, conventional fiber glass mats do not stretch enough to permit such a molded shape.
For making satellite dishes like the mini-dishes that are currently popular for residential use, it would be desirable to have a nonwoven glass fiber reinforcing mat that is conductive and that will stretch or compress with the forming stresses. It would also be desirable to have a conductive fiber glass mat that can be used to make anti-static wall coverings and carpet, RF shielding for military uses, computer enclosures, electronic uses and automotive uses.